1. Field of the Invention
The present invention relates to a DC power source unit that can selectively charge a battery pack, which is used as a power source for a cordless power tool, and supply DC voltage to the cordless power tool through an adaptor shaped like the battery pack.
2. Description of the Related Art
Cordless power tools are convenient because they can be used anywhere without being restricted by the length of a power cable. However, whenever the battery runs low, the battery pack needs to be removed and charged or else replaced with another battery pack that has already been charged.
A DC power source unit that converts alternating current to direct current can be used along with the battery pack. That is, the DC power source unit can be used when the cordless power tool is to be operated in a single place that has a source of alternating current, and the battery pack can be used when the cordless power tool is to be operated at several different places that have no source of alternating current.
However, this situation has a problem in that the operator of the cordless power tool must carry both the DC power source unit and the battery pack""s charging unit to the work area. Japanese Patent Publication No. 2000-184614(A) discloses a DC power source unit with a charging function. When the DC power source unit detects that the attached cordless power tool is being operated, it supplies power only to the cordless power tool and not for charging purposes. On the other hand, when DC power source unit detects that the cordless power tool is not being operated, then it charges a battery pack.
Here, the DC power source unit disclosed in Japanese Patent Publication No. 2000-184614(A) will be described in more detail. The DC power source unit includes a microcomputer, a DC-DC converter, and a mode switch for switching between charge of the battery pack and supplying power to the cordless power tool. When the power switch of the cordless power tool is turned ON while the DC power source unit is charging a battery pack, then the microcomputer outputs a signal for turning OFF the DC-DC converter. Once the mode switch is switched from charging the battery pack to supplying power to the cordless power tool, then the DC-DC converter is turned ON again, whereupon the cordless power tool starts operating.
However, the configuration disclosed in the above-mentioned Japanese Patent Publication has the following drawback. While a battery pack is being charged, there is a slight delay from when the operator turns ON the power switch of the cordless power tool until the cordless power tool actually starts operating. This gives the operator the sensation that something is not right.
Further, the configuration disclosed in the above-mentioned Japanese Patent Publication deals with only a single fixed rated voltage of battery pack and cordless power tool. However, in view of the fact that there are a variety of different cordless power tools that operate with different rated voltages, it is desirable that the power source unit be capable of outputting desired drive voltages that correspond to the rated voltages of a variety of different cordless power tools so that the power source unit can drive all of these cordless power tools. In addition, it is desirable that the power source unit have a charging function capable of charging a variety of different battery packs with different battery voltages.
In view of the foregoing, it is an object of the present invention to overcome the above-described problems, and provide a DC power source unit with a charging function wherein charging is stopped and supply of power to the cordless power tool is started instantaneously when the power switch of the cordless power tool is turned ON, so that the operator does not feel anything is wrong.
It is another object of the present invention to provide a DC power source unit with a charging function capable of outputting drive voltages that correspond to the rated drive voltages of a variety of different cordless power tools and capable of charging battery packs with a different battery voltages.
To achieve the above and other objects, there is provided according to one aspect of the invention a DC power source unit that can stop charging the battery pack and start supplying power to the cordless power tool instantaneously when the power switch of the cordless power go, tool is turned ON. The DC power source unit includes a switching power source for implementing an AC-DC conversion and providing a DC power; a battery pack connecting portion for connecting the battery pack to charge with the DC power provided from the switching power source; an adapter for supplying the DC power provided from the switching power source to the tool; a power source output controller for controlling the DC power provided from the switching power source in accordance with the DC power supplied to the tool and to the battery pack; a power output switching circuit for switching between supplying the DC power to the tool through the adapter and charging the battery pack; and a trigger detector for detecting that the power switch of the tool is turned ON and outputting an ON signal indicative of ON of the power switch to the power output switching circuit. In response to the ON signal, the power output switching circuit instantaneously allows the DC power to be supplied to the tool and prohibits the battery pack from being charged.
The DC power source unit according present invention supplies power to the tool, but does not charge the batter while the tool is being operated. On the other hand, the DC power source unit charges the battery pack while the tool is not being operated. More specifically, when the power switch of the tool is turned ON while a battery is being charged, then instantaneously charging operations are stopped and supply of power is switched to the cordless power tool. Therefore, the operator does not get the feeling that something is wrong.
According to another aspect of the invention, there is provided a DC power source unit that is capable of outputting drive voltages that correspond to the rated drive voltages of a variety of different cordless power tools and capable of charging battery packs with a different battery voltages. The DC power source unit includes a switching power source for implementing an AC-DC conversion and providing selective one of a plurality of different output voltages corresponding to a plurality of different drive voltages of the tools and selective one of a plurality of different charge currents corresponding to the plurality of different battery packs; a battery pack connecting portion for connecting each of the plurality of battery packs to charge with a corresponding charge current; an adapter for supplying an output voltage among the plurality of different output voltages to a corresponding tool; a voltage/current setting circuit for setting the output voltage and the charging current output from the switching power source to predetermined values; a power output switching circuit for switching between supplying the DC power to the tool through the adapter and charging the battery pack; a battery condition detector for detecting a condition of the battery pack and providing a battery condition signal; a power source output detector for detecting the output voltage and the charging current from the switching power source and also detecting that the power switch of the tool is turned ON, and for outputting a power source output detection signal; an output current detector for detecting output current from the switching power source and outputting an output current detection signal; and a controller for controlling, based on the power source output detection signal, the voltage/current setting circuit so that the voltage/current setting circuit sets the output voltage to a value corresponding to a rated voltage of the tool.